This invention relates to a method and apparatus for inspecting a rupture initiation in articles of manufacture. Although the invention will be described in connection with a rupture test on a gear, it is to be understood that the invention is not limited in any way to such application and is equally applicable to inspect a rupture initiation in power transmission components used in automotive vehicles and other articles.
Endurance tests have been conducted on power transmission components used in automotive vehicles to ensure their strength against a predetermined number of repetitive applications of a constant load. For correct detection of an initiation of the rupture of a tested power transmission component, it is necessary to inspect a small rupture such as a crack in the power transmission component.
When a force is applied to a solid brittle article, elastic energy is stored at a point where stress concentration occurs in the article. When the concentrated stress exceeds a limit, the article is subject to plastic deformation and/or small rupture at the point, causing stress relaxation to release the stored elastic energy. A part of the released elastic energy is converted in the form of elastic wave (acoustic emission) propagating through the article. A well-known acoustic emission (AE) method utilizes the elastic wave to inspect a small rupture of the article. The acoustic emission method employs an elastic wave sensor attached to the article, a signal processor and a cable connected between the elastic wave sensor and the signal processor. However, the cable is twisted and eventually broken where the article is a rotary component tested while rotating.
In order to solve the problem, there is proposed, in Japanese Patent Kokai No. 63-271132, an elastic wave sensor attached to a bearing on which the rotary component is carried. Since the elastic wave sensor is separated from the rotary component to be tested, however, the elastic wave signal obtainable from the elastic wave sensor is attenuated to a great extent and it has noises superimposed thereon.
There is also proposed, in Japanese Patent Kokai No. 63-241350, an elastic wave sensor attached to an article to be tested. The elastic wave sensor includes an FM transmitter for transmitting a elastic wave signal at FM frequencies to the signal processing unit. However, the elastic wave sensor of this type is very expensive and sensitive to vibrations. The elastic wave sensor would be damaged if it is used for a fatigue test.
Slip rings are well known in the art as inexpensive signal transmission devices. However, such slip rings operate with sufficient efficiency for frequencies less than about 10 kHz. For this reason, they have not been used to transmit an elastic wave signal from an elastic wave sensor to a signal processing unit.